"What do I eat before a fast," is quite a question to answer. In the Jewish calendar, there are two long fast days (25 hours without drink or food). I am now, referring to Yom Kippur, known as the Day of Atonement. It is a day of prayer and of course, no ingesting. It should be a difficult day but I never find it so. By the end, I am completely uplifted. (As a point of information, there are other shorter fasts.)
I take what we eat and drink before the fast seriously and weigh out all choices. We need fillers and we need food with little spice so that we are not thirsty. I came up with a pretty good meal, in my humble opinion, for out family and guests.
My youngest daughter made chicken in a mild duck sauce. I made the sides and salads and I bought dessert. (The latter is a secret) For one of the sides, I made this Scalloped Potatoes and Onions, originally a Taste of Home recipe. I did make some changes.